The present invention relates generally to methods and instruments for treating pseudoarthrosis.
Back pain affects millions of individuals and is a common cause of disability for the middle-aged working population. A frequent cause of back pain is rupture or degeneration of intervertebral discs. In many instances, the only relief from the symptoms of these conditions is a discectomy, or surgical removal of all or a portion of an intervertebral disc. Additionally, the disc space height must be maintained or restored.
One solution to the stabilization of an excised disc space is to fuse the adjacent vertebrae between their respective endplates. Typically a spacer or implant is inserted into the treated or prepared disc space until complete arthrodesis is achieved. The spacer/implant must provide temporary support and allow bone ingrowth. Success of the discectomy and fusion procedure requires development of a contiguous growth of bone or an osseous bridge to create a solid mass between the vertebrae to withstand the compressive loads on the spine for the life of the patient.
Several metal spacers have been developed to fill the void formed by the discectomy and to promote fusion. Sofamor Danek Group, Inc., (Memphis, Tenn.) markets a number of hollow spinal cages, and a wide variety of other such cages are known in the art. For example, U.S. Pat. Nos. 5,015,247 and 5,984,967 to Michelson et al. and Zdeblick et al., respectively, disclose threaded spinal cages. The cages are hollow and can be filled with osteoinductive material, such as autograft and allograft, prior to insertion into the intervertebral disc space. Apertures defined in the cages communicate with the hollow interior to provide a path for tissue growth between the vertebral endplates.
Although some success with respect to spinal fusions has generally been obtained with respect to interbody fusions or intertransverse process fusions, the incidence of pseudoarthrosis, also known as pseudarthrosis, or failure of a spinal fusion, may be relatively high in certain circumstances. For example, the incidence of pseudoarthrosis has been reported as high as 40% for smokers, as well as for patients having multilevel fusions and unrecognized metabolic disease. Pseudoarthrosis has been shown to be the contributing cause of symptoms in 78% of symptomatic patients requiring reoperation, with each reparative procedure decreasing the probability of success. Moreover, at least about 90% of attempted posterolateral intertransverse process fusions with autogenous iliac crest bone grafting in Lewis rats fail.
In order to treat symptomatic pseudoarthrosis, a conventional, open surgical procedure includes direct exposure of the fusion mass, decortication, bone regrading and possibly reinstrumentation or addition of new graft and/or new instrumentation. The repair procedure can be very complex, is highly invasive and additional posterior fusion procedures may need to be performed to stabilize the spine after a fusion has failed. Thus, simpler, less invasive methods for treating spinal pseudoarthrosis are needed.